Gone to taffy jetting-still have a midrange bog!

41 replies to this topic
  • michaeltrundle

Posted August 27, 2002 - 01:10 PM


I don't know how you do it mate!
I dropped the needle down 1 notch to pos 2 and it definately has made an improvement to the midrange
punch. She pulled some good wheelstands on the way to work this morning in 3rd and 4th but I still dont really have the upper midrange/topend power back yet.It pulls through the midrange pretty well but starts to flatten off up top, if you know what I mean. Once I get up to about 80kmh I can't get it to stand up, even when using the clutch. I used to be able to pull it into a mono at 90-100 kmh just by nailing it.
I couldn't get it to pop or backfire either under power or decel so I think I may be heading in the right direction. The pilot area still seems good, she still does the little snap wheelies in 1st or 2nd pretty well. I suppose my next step is to go from the 158 main to a 155.

Okieguy- thanks for the info on your bike, It seems I am heading in the direction of your jetting and will probably end up with the same or similar settings.Do you run YZ timing or WR with that jetting?
Any other suggestions or advice much appreciated.

  • Taffy

Posted August 27, 2002 - 08:26 PM



go down on the MJ in two tests.

the first is a straight 155MJ and then try a 152MJ. the needle lower will either crispen up; much to your pleasure or it'll go lean and the bike'll vibrate but not go forward.

in which case don't lift the needle a clip. lift it half a clip by using a washer.

that should do it. if your pipe is the tops then your jetting will be just about there.


  • michaeltrundle

Posted August 27, 2002 - 08:54 PM


I hear ya!
Will drop in to the bike shop and grab a 155 mj and see how that goes.
Thanks again for your advice.

  • michaeltrundle

Posted August 28, 2002 - 12:57 PM


I put the 155 main in last night and it feels REALLY GOOD!!!
The bitumen was a bit wet this morning so I had to take it pretty easy but it feels nice and smooth, the top end is pretty much back to what I had with the bigger jets, probably a bit better.
I will try a 152 as well and see if that makes much more of a difference. The throttle response is much better than its ever been without a bog or stumble to speak of. Cant wait to try it in the bush on the weekend.
Thanks for making me do a 180 and leaning it off instead of going richer like I was going to.
I cant believe you live on the other side of the world and you can give me advice that always seems to be right on the money!
Where would I be without the thumpertalk gurus?
Can't thank you enough.

  • Taffy

Posted August 28, 2002 - 09:13 PM



one of the hardest things to test is the difference between the MJ and the needle. you have to have a good bit of road that may even have a slight incline and do lots of "roll on for a second, blip back , roll on for a second, blip the throttle back and go again, and so forth. also straight forward 60mph to flat out tests.

as i suspected the needle was rich and the MJ has leaned it off nicely for you.

this as said previously will mean that with more of the needle straight in the hole; your PC is now slightly leaner.

if this was slightly rich then that will also be an improvement!


  • michaeltrundle

Posted August 29, 2002 - 12:16 AM


I came home from work today and swapped the 155 for 152 and went back out and terrorised the neighbourhood for a while. It felr pretty good and snappy but didn,t seem to have quite the same torque or pull once the revs got wound up towards highway speeds. It was hard to pull a top gear wheelie or even a fourth gear one. When I would first roll it on the front wheel would lift like she was going to pull up into a nice wheelie but it didn,t seem to have the power further up to keep the wheel coming up like it should. The missus was still at work after I got back so I went and put the 155 back in and went out for a back to back comparison. The 155 definately Feels better up high. Top speed came around much much quicker and it will pull up into a wheelie at 100km an hour again.
A lot more grunt up high and revved out faster. The only small problem, is that below about, half throttle doesn,t feel quite as crisp or clean as it was with the 152 main. I didn't think the main would make that much difference down in the bottom end-midrange area. There isn,t really that much difference but enough to for a nittpicker like me to notice.
I will have a play with the fuel screw tomorrow and see if I can get it to crispen up a bit more down low. I noticed once or twice as I pulled in the clutch coming to a stop, if I gave it a really quick blip, it didn,t seem to respond at all, just a bit of a blubber or a cough.
Would you recommend that I drop the needle right down to pos 1 to try and clear up the bottom half of things, or is being at one extreme or the other an indication of something else being wrong?
Is there a better needle I should be using or is the 'ELN' still a good'n?
I think its probably worth waiting till I go to YZ timing (saturday morning) and see if I need to iron out any little jetting issues after I've ridden it like that. Would you agreee?
I think I,m getting pretty close to perfect now and most people would probably not even notice what I am whingeing about but I get annoyed by poorly tuned engines, especially when they live in my shed.
Hope the yz timing issue is as good as its cracked up to be. If it makes as much difference as being jetted properly does, then I'll be stoked.

  • Taffy

Posted August 29, 2002 - 08:34 AM


i hear ya

well the 155 sounds good doesn't it! it's probably crispened up the top 3/4-full and the needle has come better through default.

your needle is now like the little dutch boy and plugging that hole in the dyke. that and the elN (NNNNNNNNNN) are why you have a slight hesitancy at tickover.

you should go by the twist of the wrist when you ride it and not go GPO paddock stand racing-anyone can do that and i think you know better than that. infact i'm sure you do.

you could alleviate some of this with a slightly larger PJ (w/o changing the PA). but i think that you may need to go to an EMM needle and lean the PC right out to 35/45PA like i have.

infact the more that i think of it the more absolutely certain of it i am.


  • michaeltrundle

Posted August 29, 2002 - 01:13 PM


I noticed this morning that If I turn the fuel screw all the way in till it bottoms out, the engine still idles ok. From what I remember this is a definate sign of being too rich on the pilot. (yes it looks like your diagnosis is correct again)
I'm going to have to order in the 35 pilot jet and adjust the paj to a 45 as you recommend.
Why do you say 45 for the paj as compared to 55 as you have in your signature?
I will order an EMM needle as well today but that will probably take a few days to get here.
Will do the yz timing swap tomorrow morning and see how she goes. I'm really hoping that I can get a good combination of the low down crisp responsive feel, with the eye watering top end as well.
Are there any tricks to ordering an EMM needle as far as dodgy part numbers etc. are concerned.
I've seen some posts concerning needle ordering problems, thats all.
Thanks again for guiding me in the right direction.
you're a legend taffy!

  • Taffy

Posted August 30, 2002 - 07:46 AM



i ran the PJ/PAJ numbers all the way down and noted that i never lowered a PAJ first. i only did it when i hit the 20mph judder!

so having finished with and sold the bike at the same time as "the missile" became the first bloke to copy my settings i asked him and others to put the PAS in the middle of the extremes at #45 and it worked.

the needle is the real problem and the EMM will cure it. there was a YZ250 needle that was ELM i believe that you can order. this is on jetting Qs by JD. go check.


  • michaeltrundle

Posted August 30, 2002 - 03:04 PM


I have an emm needle ordered and a 35 pilot jet as well. Should be here the day after tomorrow.
What is the best way to go about the next phase. Do you think I should put the new pilot jet in and see how that goes or swap needles first or both at once? I think one at a time is the way to go but I'm only really an amateur at this.
Should I start in the middle clip pos on the EMM or am I going to be better off starting closer to one end or the other?
Sorry to keep dragging you back into jetting issues but you seem to give the best advice.
The local tuners/mechanics are still on the
'48 pilot/172 main' bandwagon. They shake their heads and cant believe that I am using the size jets that I am. I'm sure they'll change their minds once the have a ride on it after I'm done.
thanks again

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  • Taffy

Posted August 30, 2002 - 09:32 PM



fit the EMM first in the same clip position as the ELN. the ELN is 1/2 clip richer and we want to lean it off the 1/2 clip if any so if you're on c2 go to c2 with the EMM and it's therefore the equivelant of 1/2 leaning off. i suspect that you could even go down to c1 here so that should be your second test.

from there some of your first yard hiccup should disappear and you may find that you need no choke etc.

even when you need choke it'll eight-stroke after about 4 seconds. time for a new (smaller) choke jet!

you'll also be running richer not at 1/4 throttle so much but in the tickover/pullaway area. so the 35/45 combo is imminent.

be careful of that MJ though because i was running a 148MJ at the end and an open pipe is worth about 8 so the 155MJ at sea level sounds right.

what you can also do for me is try a colder plug when all this is done. but you must get the choke spot on first. seriously!!

so get yourself a 9 next time your'e out, ok?


  • michaeltrundle

Posted September 02, 2002 - 01:36 PM


I stuck the EMM in on pos.2 and shortened my ap stroke a litlle bit more. The bk screw must have moved a little and the squirt was nearly 1 sec. long. I have it back to a bit less than .5 sec.
Coming to work it felt ok through the mid but it still feels a bit rich right at the bottom like you said it would. When I cruise along in top gear and at a constant speed with it just cracked open a little it sounds a bit blubbery and rich still. Snapping it open from fully closed still causes a short but evident bog and then she takes off.
I will try and drop the needle to pos 1 today and see if it clears it up at all. I have the 35 pilot at home so If dropping the needle doesn,t clean it up I will put it in tonight and see how that goes.
I think I will need to go to the 35 pj to get it really crisp down low, but will try the needle first I guess.
getting closer every time.

  • michaeltrundle

Posted September 02, 2002 - 06:17 PM


I dropped the needle down to pos 1 and went for a quick ride at lunchtime. It felt a bit crisper off idle but if I ride along at about quarter throttle and then roll it open really quickly I get a really bad stumble at about half throttle or thereabouts. It's really hard to pull into a wheelie and doesn,t have the 'grunt' it used to. If I snap it open from fully closed pretty much the same thing happens. The stumble definately feels like it is occuring at a wider throttle opening than the bottom end bog I am trying to eliminate.
I think I may have to lift the needle back up a notch or two to get the midrange to come back, as well as putting the 35pj/45paj combo in to clean up the 'off idle response'.
Sound like a good plan to you or what?

  • Taffy

Posted September 02, 2002 - 08:50 PM


yep have a go.

sounds rich but from here it's hard to be sure. one thing i'm sure of is that that 35PJ will be a good idea.


  • michaeltrundle

Posted September 04, 2002 - 01:42 PM


Ok, I put the 35 pilot/45paj in and lifted the needle up to pos 3. in an attempt to get rid of the mid throttle bog.
The bottom end, just off idle is really nice and crisp and clean.
BUT!!! I still have a really bad cough when rolling it on quickly. Either from fully closed or from a constant throttle opening.
If I,m cruising along in top gear at 60-80 kmh at approx 1/8-1/4 throttle and snap it open across the 1/4 to 3/4 throttle range she just seems to pause for a half a second and then takes off.
It (the hiccup) feels almost identical to the previous 38pj/60paj with the EMM needle in pos 1.which was definately worse than the previous test with the needle in pos 2.
It is a really bad hiccup and I wouldn't want to try to ride it on the trails like it is now. I am back to being almost unable to pull a wheelie at all.
I'm starting to get a bit confused with this midrange problem I have developed. From what I can tell the pilot feels the best its been so far, but the midrange hiccup that I have, by far outways any gains I have made in the pilot area.
The main still feels ok once I get wound up.
please help!

  • michaeltrundle

Posted September 04, 2002 - 07:20 PM


I lifted the needle back up to pos 4 and the bog is almost completely gone. I really have to try and catch it off guard and snap it open really quick to get any sort of hiccup to occur and it rarely does occur.
The 35 pilot makes it nice and clean and snappy down low (very happy with that area)and the midrange wheelstands are almost back to normal.
The upper midrange/topend area feels a little bit flat though.
I think I will try clip 5 tonight and see if it gets better still.
I also want to try going back up to a 158 main and leaving the needle in pos 4. to see if that will give me a bit more midrange/topend power.
I removed the spark arrestor gauze when I did the yz timing swap on the weekend, which was after I had done the main jet tests.(stupid me)
Not exactly the most methodical approach to jetting I know, but I thought what the hell, I want to see how much power and response I can get, and I dont want to have to go through this again next time I pull the gauze out for a race etc.
I will post results after I try the above mentioned changes.
thanks for your help taffy,I am getting very very close to the perfectly jetted 4 stroke now.

  • Taffy

Posted September 04, 2002 - 08:51 PM


i did say that the MJ is hard to read and that you need to be sure. crispness v power; they're two different things. but it sounds like you've got it under control at the moment so well done.

i would think that 158MJ and c3 sounds near.


  • michaeltrundle

Posted September 04, 2002 - 11:56 PM


Ok so now its really close.
I put the 158 main in and took it back out for a good flogging this evening and now she's really starting to boogie!!
Wheelstands at 100kmh in fourth without having to yank on the bars or grab for some clutch are a piece of cake. Lots more torque again.I guess that spark arrestor gauze makes one main jet size difference 155 to 158.
The only small issue I could notice was if I cruised along at highway speed(90-100kmh)at a small throttle opening and gently eased off the power, or crested over a hill and started to take the load off the engine, so to speak, it did a tiny bit of blubbering or missing , not really loud popping or backfiring just sort felt a bit fluffy or blubbery, like it was a big two stroke and needed a bit of load on it to make it run smoothly.
If I backed off hard it was normal smooth deceleration without any popping etc. at all. I suppose that might be an indication of the needle being one clip too rich, which would mean I would end up at 158main and c3 as you suggested taffy,
I might try to adjust the fuel screw a bit and see if that clears it up first. I,m getting a bit sick of pulling that carb off. Timed my needle change at 12 minutes from start to finish today, and that means I've had too much practice.
thank you again.

  • MN_Kevin

Posted September 05, 2002 - 01:59 AM


Please update your signature w/ your final jetting specs (including clip position) when you feel your jetting is great.

It REALLY helps the new guys trying to sort things out.

Thanks Mate!


  • Taffy

Posted September 05, 2002 - 03:05 AM


you should have done those snap wheelie tests everytime you changed a pilot setting.

the PS won't help you where you're going!!! you're damned!! it's needle or nowt now.

if you find the whole thing too viscious you can try the DTM needle back in it. it would be a bit crisper at low speeds in first and second whilst the 3/4 throttle would diminish slightly.

you can also have one last try at that APJ if needs be but at .5 seconds i found i couldn't make it any shorter without it stopping from functioning even.



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